Fuel systems for gas turbine engines



March 26, 1968 T. c. YATES FUEL SYSTEMS FOR GAS TURBINE ENGINES FiledJune 9, 1966 ELECTRICAL THROTTLE E L E C TRON/ C CONTROL MANUAL SELECTORP w P United States Patent Ofifice 3,374,622 Patented Mar. 26, 19683,374,622 FUEL SYSTEMS FOR GAS TURBINE ENGINES Thomas Charles Yates,Solihull, England, assignor to Joseph Lucas (Industries) Limited,Birmingham, England Filed June 9, 1966, Ser. No. 556,442 2 Claims. (Cl.60-3928) ABSTRACT OF THE DISCLOSURE A fuel system for a gas turbineengine having a throttle arranged on the downstream side of a fuel pumpand 'an engine speed reponsive governor for protecting the engine fromoverspeeding by limiting the amount of fuel delivered. A main manuallyoperable power means for varying the throttle setting and an auxiliarymanually operable power means for varying the throttle setting due tofailure of the main power means are provided. Also included are meansenergized when the auxiliary power means is energized and responsive tochanges in the throttle setting and arranged to modify the response ofthe governor to engine speed.

This invention relates to fuel systems for gas turbine engines and ofthe kind comprising a fuel pump which is capable of delivering fuel tothe engine through a throttle, an engine-speed responsive governor forprotecting the engine against overspeeding by limiting the quantity offuel delivered thereto, a main manually operable power means for varyingthe setting of the throttle in accordance with certain predeterminedrequirements, and an auxiliary manually operable power means also forvarying the setting of the throttle, with said auxiliary power meansbeing intended for use in the event of failure of the main power means.

The object of the present invention is to provide a fuel system of thekind specified, in a convenient form.

According to the present invention, a fuel system of the kind specifiedis characterized by the provision of apparatus energized when theauxiliary power means is energized, and being responsive to changes inthe throttle setting to modify the response of the governor to enginespeed.

A specific example of the invention will now be described with referenceto the accompanying drawing which is a diagrammatic representation of afuel system for a gas turbine engine for installation in an aircraft.

In this example the fuel system comprises a variable stroke swash-platetype pump for delivering fuel to burners 11 in an engine 12, the fuelbeing supplied from a tank 13. There is a throttle 14 disposed in supplypipe 15 between the pump 10 and the burners 11, and the stroke of thepump 10 is controlled by a piston and cylinder type servo mechanism 16one end of which is subjected to pump inlet pressure and this end alsocontaining a spring, and the other end of the mechanism 16 is subjectedto the pressure at the downstream side of the pump as modified by avalve 18, through a pipe 19.

This valve 18 per se is responsive to changes in the pressure dropacross the throttle 14. Fuel in the pipe 19 can also reach the inlet ofthe pump 10 through a restriction 20. With this arrangement, should thequantity of fuel delivered by the pump exceed that which can pass thethrottle 14, the excess fuel will be spilled through the valve 18 andwill also exert a pressure on the servo mechanism 14 to reduce the pumpstroke until the correct quantity of fuel is being delivered to theengine. The pump stroke is likewise increased if the quantity of fuelbeing delivered is inadequate.

The system also has a further valve 21 which can also permit How of fuelfrom the supply pipe 15 through the restriction 20 to the pump inlet.This valve 21 is operated by an engine speed responsive governor 22which, in this example is of the fly-weight type, and has springs 23aand 23b, the loading of which determine the engine speed at which thevalve 21 opens, with the valve and governor being rotatable by theengine 12 through suitgearing indicated by numeral 24.

The system also includes main power means for varying the setting of thethrottle 14, comprising a manually operable selector 25 for energizingan automatic electronic control 26 incorporating means responsive to thevarious functions which dictate safe engine control during acceleration,deceleration and steady running conditions of the engine. The main powermeans also includes an alternating current electric motor 27 which isconnected to the throttle 14.

The system further includes an auxiliary power means in the form of adirect current electric motor 28 which can be run at a slow speed underthe direct control of the aircraft pilot through a button 29. This motor28 cannot be run at a speed which will induce stalling of the engine dueto excess fuelling. The auxiliary power means for setting the throttle14 is part of an emergency stand-by system in an aircraft, for use inthe event of the failure of the main power means and is supplied from aseparate power source (not shown). The two motors 27 and 28 are capableof moving the throttle 14 independently and the drive takes placethrough a leverage mechanism 30 or alternatively through a differentialgearbox.

For use only when the auxiliary power means is energized, there isprovided apparatus comprising a device 31 which in this example, is avariable inductance but may alternatively be a variable capacitance,which senses changes in the setting of the throttle 14 and generates anelectrical signal which is fed to an electrical control unit 32 arrangedto energize an electric motor 33 which, in turn varies the position of acam 34 which engages a movable abutment 35 for the spring 23a of thegovernor 22.

With this arrangement, changes in the throttle setting are used to varythe response of the governor 22 to engine speed and thus the speed atwhich the valve 21 will open to permit spill. It will be appreciatedthat normally, when the main power means is in operation, the governor22 acts as a topspeed governor only, but when the auxiliary power meansis in use, the governor 22 response is modified to minimize the risk ofoverspeeding at throttle settings below the maximum as well as at themaximum speed of the engine.

When the auxiliary power means is in operation due to failure of themain power means, or for any other reason, the pilot can thus select anyfuel flow rate as may be required under varying conditions.

At a point during throttle movement, the engine speed ceases to bedetermined solely by the fiow permitted by the throttle and isdetermined at least in part by the governor 22. The engine speed atwhich this occurs is dependent upon aircraft speed, altitude, andclimatic conditions. In most instances the upper 10% of the speed rangeof the engine is subject to control by the governor 22, this being therange over which, most of the time, an aircraft engine is run. Thusspeed selection over this range is by the pilots button 29 but thegovernor 22 ensures that the selected speed is maintained substantiallyconstant. The invention is not to be confined to any strict conformityto the showings in the drawings but changes or modifications may be madetherein so long as such changes or modifications mark no materialdeparture from the spirit and scope of the appended claims.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A fuel system for a gas turbine engine comprising a fuel pump, athrottle arranged on the downstream side of the pump, an engine speedresponsive governor arranged to protect the engine from overspeeding bylimiting the amount of fuel delivered thereto, a main manually operablepower means for varying the throttle setting, an auxiliary manuallyoperable power means for varying the throttle setting in the event offailure of the main power means, and apparatus energized when theauxiliary power means is energized, and responsive to changes in thethrottle setting to modify in variable manner the response of thegovernor to engine speed.

2. The fuel system as claimed in claim 1 in which said governor isprovided with biasing means and said apparatus includes electricalsignal producing means, with said signal being responsive to changes inthe throttle setting, and said signal being transmitted to a device forvarying the biasing means of the governor, changes in said biasing meansvarying the response of the governor to engine speed.

JULIUS E. WEST, Primary Examiner.

